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Abstract

This paper considers effect of variation in value of Discharge current on different process parameters of Die Sinking EDM. The parameters considered were Material removal rate (MRR), Tool removal rate (TRR), Surface roughness (Ra) and Time (for machining required depth of cut). A total of 32 experiments were conducted on four different hard steels i.e. Die steel D3, En-8, En-19 and Stainless steel (SS-AISI-440C). The Copper and Aluminium electrodes brazed with mild steel were used for machining. The four different values of current i.e. 6A, 9A, 12A and 15A were considered for the study. The experimental results shows the relationship between MRR, TRR, Ra and Time with variation in magnitude of discharge current. This study also illustrates the relationship among different process parameter considered in the study. The results are shown with the help of graphs and tables.

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Introduction

EDM has been an important non-conventional machining process (Singh et al., 2004) widely used in manufacturing of hard and complex 3-D geometries which are difficult to machine by conventional machining processes (Pawade & Banwait, 2013; Chryssolouris, 2005). In EDM there is no direct contact between the tool and the workpiece (Khan et al., 2015) as a result mechanical stresses, vibrations and chatter problems are eleminated (Tsai et al., 2003). The electrode and workpiece must be conductor of electricity in order to generate spark (Abbas et al., 2007). EDM removes material with good accuracy and process is characterized by slow processing speeds. It is reproductive shaping process in which the shape of tool electrode is mirrored in the workpiece (Konig et al., 1988).

In past few decades research has been focused on optimising the process parameters of EDM (Salonitis et al., 2009). Kiyak & Cakir (2007) presented a study on influence of EDM parameters on surface roughness for machining of 40CrMnNiMo864 tool steel (AISI P20). The parameters selected were pulsed current, pulse time and pulse pause time. It was observed that higher value of these parameters increases surface roughness. Tang & Guo (2014) performed parameter optimization of S-03 stainless steel on EDM. The process parameters considered were gap voltage, peak discharge current, pulse width and pulse interval whereas MRR and Ra were objective parameters. Pellicer et al., (2011) presented a study on influence of EDM process parameters and tool geometries on basic process performance measures. Experiments were conducted with varying parameters in H13 steel using different geometries of copper electrodes.

Ghoreishi & Tabari (2007) examined the effect of voltage excitation of the pre-ignition spark pulse on the process outputs including material removal rate (MRR), electrode wear ratio (EWR) and surface roughness (Ra). The results shows that applying voltage excitation of the pulse produces effective pulses, which decrease EWR and Ra and increases MRR. The cooling effect of copper electrode on electric discharge machining of titanium alloy (Ti-6Al-4V) has also been analysed (Abdulkareem et al., 2009). The machining parameters considered were current intensity, pulse on-time, pulse off-time and gap voltage while the electrode wear and surface roughness were the process responses. A study on MRR and EWR on powder mixed electrical discharge machining (PMEDM) of Cobalt-bonded tungsten carbide (WC-Co) has been carried out by authors in (Kung et al., 2009). The machining parameters considered for evaluation of MRR and EWR were discharge current, pulse on-time, grain size and concentration of Al powder.

In this study Die Sinking EDM (PS LEADER ZNC) was used to conduct experiments. A view of PS LEADER ZNC EDM is shown in Figure 1. This study examines the effect of variation of Discharge current on Material removal rate (MRR), Tool removal rate (TRR), Surface roughness (Ra) and Time (for machining required depth of cut) in machining of Die steel-D3, En-8, En-19 and Stainless steel (SS-AISI-440C). This study also illustrates a comparative analysis of different process parameters with the help of statistical graphs. The Copper and Aluminium (16mm*24mm) electrodes were selected for machining of the workpieces (Gaitonde et al., 2010; Kumar et al., 2012). Upper part of the electrode is made of mild steel which is brazed to the copper and aluminium pieces to form the tool electrode. The polarity used for the experiments is reversed polarity i.e. tool electrode is given positive polarity and work piece is given negative polarity (Banker et al., 2013).